PURPOSE: Based on the logic that self-oriented perfectionism (SOP) is one of the most well-established predictors of academic procrastination (AP), we predicted that fear of failure (FF) would mediate the association between SOP and AP. The purpose of this study is to investigate the mediating effect of FF on the influence of SOP on AP in medical students. METHODS: A total of 156 undergraduate medical students completed a battery of questionnaires. This study is an analysis of cross-sectional data obtained through an offline survey. The self-report questionnaires assessed demographics and psychological scales, including the Multidimensional Perfectionism Scale, Performance Failure Appraisal Inventory, and Aitken Procrastination Inventory. The data were analyzed by descriptive statistics, correlations analysis, and multiple regression analyses using IBM SPSS ver. 22.0 (IBM Corp., Armonk, USA). RESULTS: SOP had a direct negative influence on AP (β=-0.420, p<0.001). Also, SOP had a significant indirect effect on AP through FF (β=0.0393; 95% confidence interval, 0.040-0.0936). These results indicated that the FF partially mediates the relationship between SOP and AP. CONCLUSION: Although SOP among medical students might play an adaptive role to lessen AP, in cases FF gets higher, SOP could have opposing effects via the mediating effect of FF, leading to an actual increase in AP. Attempts to deal with the FF among medical students should be made for better academic achievements.